Hybrid vehicle and control method therefor

ABSTRACT

In a hybrid vehicle, motor traveling using only an output of a rotating electric machine utilizing electric power of a vehicle-mounted power storage device is applicable in a region inside a maximum output line in motor traveling for an EV mode, and in a region inside a maximum output line in motor traveling for an EV mode. Each of the maximum output lines is composed of straight line portions defining an upper limit torque and an upper limit vehicle speed and a curved line portion defining upper limit output power, in motor traveling. Therefore, if a vehicle speed exceeds the upper limit vehicle speed in motor traveling in each of the EV mode and the HV mode, an engine is started. A motor traveling upper limit vehicle speed in the EV mode is set to be lower than a motor traveling upper limit vehicle speed in the HV mode.

This is a 371 national phase application of PCT/JP2010/060854 filed 25Jun. 2010, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a hybrid vehicle and a control methodtherefor, and more particularly to traveling control for a hybridvehicle allowing selection between traveling using only an output of arotating electric machine and traveling using outputs of the rotatingelectric machine and an engine.

BACKGROUND OF THE INVENTION

Hybrid vehicles configured such that a rotating electric machinegenerates a vehicle driving force using electric power from a secondarybattery mounted in a vehicle have been attracting attention.

Japanese Patent Laying-Open No. 2008-285011 (PTL 1) describes a hybridvehicle in which selection is made between a mode in which the vehicletravels by operating at least an engine and a mode in which the vehicletravels by stopping the engine and using only an output of a motorgenerator. PTL 1 describes that, in the hybrid vehicle, replacementtiming of consumable parts related to the engine is determined based onan operation result of the engine.

Further, hybrid vehicles require traveling control which can avoidexcessive charging/discharging of a vehicle-mounted secondary batteryand also ensure driving performance in response to a driver's request.Japanese Patent Laying-Open No. 2006-109650 (PTL 2) describes a controldevice for a vehicle and a method for controlling a vehicle. PTL 2describes that an upper limit value or a lower limit value of the amountof change of a torque generated by a traction motor serving as arotating electric machine generating a vehicle driving force is setbased on a limit value of output power or input power of a secondarybattery and a speed of the vehicle. Thereby, it is aimed that thetraction motor outputs a torque requested by a driver without causingexcessive charging/discharging of the secondary battery.

As described in PTL 2, it is common to set upper limit values of inputpower and output power of a secondary battery based on a state of charge(SOC) and a temperature of the secondary battery. An output of atraction motor is set in a range where the output power of the secondarybattery does not exceed the upper limit value. Thus, if the output powerupper limit value is limited due to a reduction in the SOC or anincrease in the temperature of the secondary battery, the output of thetraction motor is also limited.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Laying-Open No. 2008-285011-   PTL 2: Japanese Patent Laying-Open No. 2006-109650

SUMMARY OF INVENTION Technical Problem

In a hybrid vehicle, either traveling using only an output of a rotatingelectric machine (hereinafter also referred to as “motor traveling”) ortraveling using outputs of the rotating electric machine and an engine(hereinafter also referred to as “hybrid traveling”) is used to suit thesituation. Thereby, energy efficiency is improved (i.e., fuel efficiencyis improved) by limiting operation of the engine to a high efficiencyregion while effectively using electric power stored in a secondarybattery. Further, so-called plug-in hybrid vehicles, in which avehicle-mounted secondary battery can be charged by a power sourceexternal to a vehicle, has been attracting attention as one type ofhybrid vehicle. In particular, it is aimed in plug-in hybrid vehicles toapply motor traveling using only an output of a rotating electricmachine for a long period of time.

On the other hand, when a hybrid vehicle travels at a high vehiclespeed, driving resistance is increased, and thus a high load state tendsto be caused even if the vehicle travels steadily without acceleration.Thus, if the vehicle continues traveling at a high vehicle speed usingonly an output of a rotating electric machine, there is a possibilitythat a state where an output current from a secondary battery, that is,a passing current of an electric system for driving and controlling therotating electric machine, is relatively large may be continued. As aresult, in order to suppress an increase in the temperature ofcomponents of the electric system and an increase in the load on thesecondary battery, a limit value of output power from the secondarybattery is likely to be strictly limited as described above.

Therefore, preferably, an upper limit vehicle speed in motor travelingis set, and, if the vehicle speed exceeds the upper limit vehicle speed,an engine is started to apply hybrid traveling. It is simply understoodthat setting a high upper limit vehicle speed leads to increasedopportunities for motor traveling.

However, if the upper limit vehicle speed is set too high, since motortraveling at a high vehicle speed is allowed, the state where the outputcurrent from the secondary battery is relatively large is likely to becontinued, which is likely to cause a state where the output power ofthe secondary battery is strictly limited as described above. Once sucha state is established, limitation on the output power may be continuedfor a long period of time until a reduction in the SOC and an increasein temperature are recovered. During such a limitation period, theengine may be operated more frequently than usual to ensure output andacceleration performance. Thus, there is a possibility that, by settingthe upper limit vehicle speed too high, opportunities for motortraveling cannot be ensured on the contrary, causing a reduction inenergy efficiency (i.e., deterioration in fuel efficiency) anddeterioration in emission.

The present invention has been made to solve such problems, and oneobject of the present invention is to appropriately set an upper limitvehicle speed for traveling of a vehicle using only an output of arotating electric machine, to improve energy efficiency and emissionproperty of a hybrid vehicle by appropriately ensuring opportunities formotor traveling.

Solution to Problem

According to one aspect of the present invention, a hybrid vehicleincludes a rotating electric machine for generating a vehicle drivingforce, a power storage device mounted in the vehicle, a power controlunit for performing power conversion between the power storage deviceand the rotating electric machine, an internal combustion engine forgenerating a vehicle driving force, an external charging unit forcharging the power storage device by a power source external to thevehicle, and a control device for controlling traveling of the vehicle.The control device includes a traveling mode selection unit, an upperlimit vehicle speed setting unit, and a traveling control unit. Thetraveling mode selection unit is configured to select, in response to astate of charge of the power storage device, one of a first travelingmode in which the internal combustion engine and the rotating electricmachine are used such that the vehicle travels mainly using an output ofthe rotating electric machine irrespective of a residual capacity of thepower storage device, and a second traveling mode in which the internalcombustion engine and the rotating electric machine are used such thatthe vehicle travels with the residual capacity of the power storagedevice being maintained within a predetermined control range. The upperlimit vehicle speed setting unit is configured to set an upper limitvehicle speed for traveling of the vehicle using only the output of therotating electric machine, in response to the traveling mode selected bythe traveling mode selection unit. The traveling control unit isconfigured to control traveling of the vehicle to use both of outputs ofthe internal combustion engine and the rotating electric machine, if avehicle speed exceeds the upper limit vehicle speed. The upper limitvehicle speed setting unit sets the upper limit vehicle speed in thefirst traveling mode to be lower than the upper limit vehicle speed inthe second traveling mode.

Preferably, the traveling control unit controls the rotating electricmachine and the internal combustion engine in the first traveling modesuch that, if the hybrid vehicle has a torque and a vehicle speed insidea first region, the vehicle travels using only the output of therotating electric machine, and if the hybrid vehicle has a torque and avehicle speed outside the first region, the vehicle travels using bothof the outputs of the rotating electric machine and the internalcombustion engine. The traveling control unit controls the rotatingelectric machine and the internal combustion engine in the secondtraveling mode such that, if the hybrid vehicle has a torque and avehicle speed inside a second region, the vehicle travels using only theoutput of the rotating electric machine, and if the hybrid vehicle has atorque and a vehicle speed outside the second region, the vehicletravels using both of the outputs of the rotating electric machine andthe internal combustion engine. The first and second regions are setreflecting the upper limit vehicle speed set by the upper limit vehiclespeed setting unit.

Preferably, in the first traveling mode, the upper limit vehicle speedsetting unit variably sets the upper limit vehicle speed within a rangelower than the upper limit vehicle speed in the second traveling mode,based on at least one of the state of charge and an input/output currentof the power storage device.

More preferably, the control device further includes a state-of-chargeestimation unit, a current load estimation unit, and acharging/discharging control unit. The state-of-charge estimation unitis configured to calculate an estimated residual capacity value of thepower storage device based on an output of a sensor arranged in thepower storage device. The current load estimation unit is configured tocalculate a current load parameter indicating a thermal load onequipment due to passage of the input/output current of the powerstorage device, based on the input/output current. Thecharging/discharging control unit is configured to variably set anoutput power upper limit value of the power storage device based on thecalculated estimated residual capacity value and current load parameter.In the first traveling mode, the upper limit vehicle speed setting unitvariably sets the upper limit vehicle speed, at least based on thecalculated current load parameter.

More preferably, the upper limit vehicle speed setting unit sets theupper limit vehicle speed in the first traveling mode, in accordancewith a minimum value of a first upper limit speed variably set inresponse to the current load parameter and a second upper limit speedvariably set in response to the estimated residual capacity value.

Preferably, the hybrid vehicle further includes a display unit forcausing a driver to visually recognize vehicle information. The displayunit includes a display area for displaying a vehicle speed range inwhich traveling of the vehicle using only the output of the rotatingelectric machine is applicable, at least based on the upper limitvehicle speed set by the upper limit vehicle speed setting unit.

Alternatively, preferably, the hybrid vehicle further includes a powergeneration mechanism configured to generate charging power for the powerstorage device using the output of the internal combustion engine. Inthe second traveling mode, if the residual capacity of the power storagedevice becomes lower than the control range, the traveling control unitcontrols the rotating electric machine and the internal combustionengine such that the charging power for the power storage device isgenerated by the power generation mechanism.

According to another aspect of the present invention, provided is acontrol method for a hybrid vehicle including a rotating electricmachine and an internal combustion engine each for generating a vehicledriving force, a power storage device mounted in the vehicle, a powercontrol unit for performing power conversion between the power storagedevice and the rotating electric machine, and an external charging unitfor charging the power storage device by a power source external to thevehicle. The control method includes the steps of: selecting, inresponse to a state of charge of the power storage device, one of afirst traveling mode in which the internal combustion engine and therotating electric machine are used such that the vehicle travels mainlyusing an output of the rotating electric machine irrespective of aresidual capacity of the power storage device, and a second travelingmode in which the internal combustion engine and the rotating electricmachine are used such that the vehicle travels with the residualcapacity of the power storage device being maintained within apredetermined control range; and controlling traveling of the vehicle touse both of outputs of the internal combustion engine and the rotatingelectric machine, if the upper limit vehicle speed is exceeded, inresponse to the selected traveling mode. The step of setting sets theupper limit vehicle speed in the first traveling mode to be lower thanthe upper limit vehicle speed in the second traveling mode.

Preferably, the step of selecting controls the rotating electric machineand the internal combustion engine in the first traveling mode suchthat, if the hybrid vehicle has a torque and a vehicle speed inside afirst region, the vehicle travels using only the output of the rotatingelectric machine, and if the hybrid vehicle has a torque and a vehiclespeed outside the first region, the vehicle travels using both of theoutputs of the rotating electric machine and the internal combustionengine, and controls the rotating electric machine and the internalcombustion engine in the second traveling mode such that, if the hybridvehicle has a torque and a vehicle speed inside a second region, thevehicle travels using only the output of the rotating electric machine,and if the hybrid vehicle has a torque and a vehicle speed outside thesecond region, the vehicle travels using both of the outputs of therotating electric machine and the internal combustion engine. The firstand second regions are set reflecting the upper limit vehicle speed setby the step of setting.

Preferably, in the first traveling mode, the step of setting variablysets the upper limit vehicle speed within a range lower than the upperlimit vehicle speed in the second traveling mode, based on at least oneof the state of charge and an input/output current of the power storagedevice.

More preferably, the control method further includes the steps of:calculating an estimated residual capacity value of the power storagedevice based on an output of a sensor arranged in the power storagedevice; calculating a current load parameter indicating a thermal loadon equipment, based on the input/output current of the power storagedevice; and variably setting an output power upper limit value of thepower storage device based on the calculated estimated residual capacityvalue and current load parameter. In the first traveling mode, the stepof setting the upper limit vehicle speed variably sets the upper limitvehicle speed, at least based on the calculated current load parameter.

More preferably, the step of setting the upper limit vehicle speedincludes the steps of variably setting a first upper limit speed inresponse to the current load parameter, variably setting a second upperlimit speed in response to the estimated residual capacity value, andsetting the upper limit vehicle speed in the first traveling mode inaccordance with a minimum value of the first upper limit speed and thesecond upper limit speed.

Preferably, the hybrid vehicle further includes a display unit forcausing a driver to visually recognize vehicle information. The controlmethod further includes the step of displaying a vehicle speed range inwhich traveling of the vehicle using only the output of the rotatingelectric machine is applicable on the display unit, at least based onthe set upper limit vehicle speed.

Alternatively, preferably, the hybrid vehicle further includes a powergeneration mechanism configured to generate charging power for the powerstorage device using the output of the internal combustion engine. Inthe second traveling mode, if the residual capacity of the power storagedevice becomes lower than the control range, the step of controllingcontrols the rotating electric machine and the internal combustionengine such that the charging power for the power storage device isgenerated by the power generation mechanism.

Advantageous Effects of Invention

According to the present invention, an upper limit vehicle speed fortraveling of a vehicle using only an output of a rotating electricmachine can be appropriately set to improve energy efficiency andemission property of a hybrid vehicle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a schematic configuration of a hybridvehicle in accordance with Embodiment 1 of the present invention.

FIG. 2 is a schematic configuration diagram of a motive power splitmechanism shown in FIG. 1.

FIG. 3 is a nomograph indicating the relationship among rotation speedsof an engine, MG1, and MG2 shown in FIG. 1.

FIG. 4 is a functional block diagram illustrating traveling control inthe hybrid vehicle in accordance with Embodiment 1 of the presentinvention.

FIG. 5 is a conceptual diagram illustrating design of a thermal load onequipment.

FIG. 6 is a waveform diagram illustrating one example of traveling modeselection with respect to SOC shifts in the hybrid vehicle in accordancewith Embodiment 1.

FIG. 7 is a conceptual diagram illustrating selection of motor travelingand hybrid traveling in the hybrid vehicle in accordance with Embodiment1.

FIG. 8 is a flowchart illustrating a procedure of processing fortraveling control in the hybrid vehicle in accordance with Embodiment 1.

FIG. 9 is a flowchart illustrating a procedure of processing for settinga motor traveling upper limit vehicle speed in the hybrid vehicle inaccordance with Embodiment 1.

FIG. 10 is a conceptual diagram illustrating setting of a motortraveling upper limit vehicle speed in a hybrid vehicle in accordancewith Embodiment 2.

FIG. 11 is a flowchart illustrating a procedure of processing forsetting the motor traveling upper limit vehicle speed in the hybridvehicle in accordance with Embodiment 2.

FIG. 12 is a conceptual diagram illustrating setting of the motortraveling upper limit vehicle speed with respect to a current loadparameter.

FIG. 13 is a conceptual diagram illustrating setting of the motortraveling upper limit vehicle speed with respect to the SOC of a powerstorage device.

FIG. 14 is a conceptual diagram illustrating an example of vehicle speedlimitation in motor traveling in the hybrid vehicle in accordance withEmbodiment 2.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings, in which identical orcorresponding parts will be designated by the same reference numerals,and the description thereof will not be repeated in principle.

Embodiment 1

FIG. 1 is a block diagram showing a schematic configuration of a hybridvehicle 5 in accordance with Embodiment 1 of the present invention.

Referring to FIG. 1, hybrid vehicle 5 is equipped with an internalcombustion engine (engine) 18 and motor generators MG1, MG2, and travelscontrolling outputs thereof at an optimal ratio. Hybrid vehicle 5 isfurther equipped with a power storage device 10.

Power storage device 10 is a rechargeable power storage element, and istypically composed of a secondary battery such as a lithium ion batteryand a nickel hydride battery. Alternatively, power storage device 10 maybe composed of a power storage element other than a secondary battery,such as an electric double-layer capacitor. FIG. 1 shows a systemconfiguration related to charging/discharging of power storage device 10in hybrid vehicle 5.

In a state where a system of hybrid vehicle 5 is started up (hereinafteralso referred to as an “IG on state”), power storage device 10 cansupply and receive electric power to and from motor generators MG1, MG2through power conversion by a power control unit 20.

Further, while the system of hybrid vehicle 5 is stopped (hereinafteralso referred to as an “IG off state”), power storage device 10 can becharged by a power source external to the vehicle (not shown,hereinafter also referred to as an “external power source”) throughelectrical connection via a connector portion 3. Instead of or inaddition to a commercial power source, the external power source to besupplied to hybrid vehicle 5 via connector portion 3 may be, forexample, electric power generated by a solar battery panel installed onthe roof of a house or the like. Details of charging of power storagedevice 10 by the external power source (hereinafter also referred to as“external charging”) will be described later.

A monitoring unit 11 outputs a temperature Tb, a voltage Vb, and acurrent Ib as values detecting the state of power storage device 10,based on outputs of a temperature sensor 12, a voltage sensor 13, and acurrent sensor 14 provided in power storage device 10. It is to be notedthat temperature sensor 12, voltage sensor 13, and current sensor 14comprehensively refer to temperature sensors, voltage sensors, andcurrent sensors provided in power storage device 10, respectively. Thatis, it is noted for confirmation that, actually, a plurality oftemperature sensors 12, voltage sensors 13, and/or current sensors 14are generally provided.

Engine 18, motor generator MG1, and motor generator MG2 are mechanicallycoupled via a motive power split mechanism 22. In response to atraveling situation of hybrid vehicle 5, a driving force is distributedand combined among the three components via motive power split mechanism22, and consequently driving wheels 24F are driven.

Referring to FIG. 2, motive power split mechanism 22 will be furtherdescribed. Motive power split mechanism 22 is composed of a planetarygear including a sun gear 202, a pinion gear 204, a carrier 206, and aring gear 208.

Pinion gear 204 engages sun gear 202 and ring gear 208. Carrier 206supports pinion gear 204 to be rotatable. Sun gear 202 is coupled to arotation shaft of motor generator MG1. Carrier 206 is coupled to a crankshaft of engine 18. Ring gear 208 is coupled to a rotation shaft ofmotor generator MG2 and a reduction mechanism 95.

Since engine 18, motor generator MG1, and motor generator MG2 arecoupled via motive power split mechanism 22 composed of a planetarygear, rotation speeds of engine 18, motor generator MG1, and motorgenerator MG2 have the relationship such that they are connected by astraight line in a nomograph, as shown in FIG. 3.

During traveling of hybrid vehicle 5, motive power split mechanism 22splits a driving force generated by operating engine 18 into two,distributes one driving force toward motor generator MG1, anddistributes the other driving force to motor generator MG2. The drivingforce distributed from motive power split mechanism 22 toward motorgenerator MG1 is used for an operation of generating electric power. Onthe other hand, the driving force distributed toward motor generator MG2is combined with a driving force generated by motor generator MG2 andused to drive driving wheels 24F.

Thus, in hybrid vehicle 5, selection can be made between motor travelingin which engine 18 is stopped and only an output of motor generator MG2is used, and hybrid traveling in which engine 18 is operated and both ofoutputs of engine 18 and motor generator MG2 are used.

Referring to FIG. 1 again, hybrid vehicle 5 further includes powercontrol unit 20. Power control unit 20 is configured to be capable ofperforming bidirectional power conversion between motor generators MG1,MG2 and power storage device 10. Power control unit 20 includes aconverter (CONV) 6, and an inverter (INV1) 8-1 and an inverter (INV2)8-2 corresponding to motor generators MG1 and MG2, respectively.

Converter (CONV) 6 is configured to be capable of performingbidirectional direct current (DC) voltage conversion between powerstorage device 10 and a positive bus MPL which transfers a DC linkvoltage of each of inverters 8-1, 8-2. That is, an input/output voltageof power storage device 10 and a DC voltage between positive bus MPL anda negative bus MNL are boosted or bucked bidirectionally. Buck/Boostoperations in converter 6 are respectively controlled in accordance witha switching command PWC from control device 100. Further, a smoothingcapacitor C is connected between positive bus MPL and negative bus MNL.The DC voltage between positive bus MPL and negative bus MNL is sensedby a voltage sensor 16.

Inverter 8-1 and inverter 8-2 perform bidirectional power conversionbetween DC power of positive bus MPL and negative bus MNL andalternating current (AC) power to be input to or output from motorgenerators MG1 and MG2. Mainly, in response to a switching command PWM1from control device 100, inverter 8-1 converts AC power generated bymotor generator MG1 into DC power, and supplies it to positive bus MPLand negative bus MNL. On the other hand, in response to a switchingcommand PWM2 from control device 100, inverter 8-2 converts DC powersupplied through positive bus MPL and negative bus MNL into AC power,and supplies it to motor generator MG2. That is, in hybrid vehicle 5,motor generator MG2 is configured to generate a vehicle driving force byreceiving electric power from power storage device 10. Further, motorgenerator MG1 is configured to generate charging power for power storagedevice 10 using the output of engine 18.

A system main relay 7 inserted into and connected with a positive linePL and a negative line NL is provided between power storage device 10and power control unit 20. System main relay 7 is turned on/off inresponse to a relay control signal SE from control device 100.

Control device 100 typically includes an electronic control unit (ECU)mainly composed of a CPU (Central Processing Unit), a storage unit suchas a RAM (Random Access Memory) and a ROM (Read Only Memory), and aninput/output interface. Control device 100 performs control related totraveling of the vehicle and external charging, by the CPU reading aprogram stored beforehand in the ROM or the like from the RAM andexecuting the same. It is to be noted that at least a portion of the ECUmay be configured to perform predetermined numerical/logical computationprocessing using hardware such as an electronic circuit.

As examples of information to be input to control device 100, FIG. 1illustrates temperature Tb, voltage Vb, and current Ib of power storagedevice 10 from monitoring unit 11, and a system voltage Vh from voltagesensor 16 arranged between lines of positive bus MPL and negative busMNL. Since a secondary battery is typically applied as power storagedevice 10 as described above, temperature Tb, voltage Vb, and current Ibof power storage device 10 will be hereinafter also referred to as abattery temperature Tb, a battery voltage Vb, and a battery current Ib,respectively.

Further, control device 100 continuously estimates the SOC of powerstorage device 10. The SOC represents a charged amount (amount ofresidual charge) relative to the fully charged state of power storagedevice 10, and is indicated, as an example, by a ratio of a chargedamount at present to a fully charged capacity (0 to 100%).

Here, a configuration for external charging will be described.

Hybrid vehicle 5 further includes a connector receiving portion 35 andan external charging unit 30 for charging power storage device 10 by theexternal power source.

In order to externally charge power storage device 10, connector portion3 is coupled to connector receiving portion 35, and thereby electricpower from the external power source is supplied to external chargingunit 30 through a positive charge line CPL and a negative charge lineCNL. Further, connector receiving portion 35 includes a couplingdetection sensor 35 a for detecting a state of coupling betweenconnector receiving portion 35 and connector portion 3, and controldevice 100 detects that a state where power storage device 10 can becharged by the external power source has been attained, based on acoupling signal CON from coupling detection sensor 35 a. It is to benoted that the present embodiment illustrates a case where asingle-phase commercial AC power source is employed as the externalpower source.

Connector portion 3 constitutes a coupling mechanism for supplying theexternal power source, typically such as a commercial power source, tohybrid vehicle 5. Connector portion 3 is coupled to a charge station(not shown) provided with the external power source, through a powerline PSL formed of a cab tire cable or the like. During externalcharging, connector portion 3 is coupled to hybrid vehicle 5, andthereby electrically connects the external power source to externalcharging unit 30 mounted in hybrid vehicle 5. On the other hand, hybridvehicle 5 is provided with connector receiving portion 35 for receivingthe external power source coupled to connector portion 3.

External charging unit 30 is a device for charging power storage device10 by receiving the electric power from the external power source, andis arranged between positive and negative lines PL and NL and positiveand negative charge lines CPL and CNL.

Further, external charging unit 30 includes a current control unit 30 aand a voltage conversion unit 30 b, and converts the electric power fromthe external power source into electric power suitable for chargingpower storage device 10. Specifically, voltage conversion unit 30 b is adevice for converting a supply voltage of the external power source intoa voltage suitable for charging power storage device 10, and istypically composed of a winding transformer having a predeterminedvoltage transformation ratio, an AC-AC switching regulator, or the like.Further, current control unit 30 a rectifies an AC voltage converted byvoltage conversion unit 30 b to generate a DC voltage, and controls acharging current to be supplied to power storage device 10 in accordancewith a charging current command from control device 100. Current controlunit 30 a is typically composed of a single-phase bridge circuit or thelike. It is to be noted that, instead of the configuration includingcurrent control unit 30 a and voltage conversion unit 30 b, externalcharging unit 30 may be implemented using an AC-DC switching regulatoror the like.

It is to be noted that, instead of the configuration shown in FIG. 1,the external power source may be received by a configuration in whichelectric power is supplied by means of electromagnetic coupling withoutcontact between the external power source and the vehicle. Specifically,it is possible to apply a configuration in which a primary coil isprovided on an external power source side and a secondary coil isprovided on a vehicle side, and electric power is supplied utilizingmutual inductance between the primary coil and the secondary coil. Thus,in applying the present invention, the configuration for externallycharging the hybrid vehicle is not particularly limited.

Since power storage device 10 can be externally charged in hybridvehicle 5 as described above, it is preferable in terms of energyefficiency that the vehicle travels with engine 18 being maintained at astopped state as much as possible. Therefore, hybrid vehicle 5 selectsone of two traveling modes, that is, an EV (Electric Vehicle) mode andan HV (Hybrid Vehicle) mode, for traveling.

Until the SOC of power storage device 10 becomes lower than apredetermined mode determination value, hybrid vehicle 5 selects the EVmode, and travels mainly using only the driving force from motorgenerator MG2. Since there is no need to maintain the SOC in the EVmode, an operation of generating electric power in motor generator MG1by receiving the driving force of engine 18 is basically not performed.It is to be noted that, although the EV mode is intended to improve afuel consumption rate by maintaining engine 18 at the stopped state,engine 18 is allowed to be started up if a request for a driving forcefor acceleration or the like is provided from a driver, if a requestunrelated to the request for a driving force, such as a request forcatalyst warm-up or air conditioning, is provided, if other conditionsare satisfied, or the like.

If the SOC of power storage device 10 is reduced to the modedetermination value during the EV mode, the traveling mode is switchedto the HV mode. In the HV mode, power generation by motor generator MG1is controlled such that the SOC of power storage device 10 is maintainedwithin a predetermined control range. That is, engine 18 is also startedfor operation in response to the start of power generation by motorgenerator MG1. It is to be noted that a portion of the driving forcegenerated by operating engine 18 may be used for traveling of hybridvehicle 5.

In the HV mode, control device 100 determines target values for therotation speed of engine 18, a power generation amount of motorgenerator MG1, and a torque of motor generator MG2, based on signalsfrom sensors, the traveling situation, an accelerator pedal position,and the like, in order to optimize overall fuel efficiency.

Further, in hybrid vehicle 5, a traveling mode can also be selected by auser operating a selection switch 26 provided in the vicinity of adriver seat. That is, the user can forcibly select the HV mode or the EVmode by inputting an operation to selection switch 26.

Hybrid vehicle 5 further includes a display unit 102 for causing thedriver to visually recognize vehicle information. Display unit 102 istypically composed of a display panel provided in front of the driver.For example, indicators indicating various types of information, such asa speedometer for indicating a vehicle speed and a fuel gauge indicatinga residual fuel amount, are displayed in display unit 102. Preferably,display unit 102 is provided with a display area 105 for displaying avehicle speed range in which hybrid vehicle 5 can perform motortraveling, as described later.

Concerning the correspondence between the embodiment of the presentinvention shown in FIG. 1 and the invention of the present application,power storage device 10 corresponds to a “power storage device”, motorgenerator MG2 corresponds to a “rotating electric machine”, engine 18corresponds to an “internal combustion engine, and motor generator MG1corresponds to a “power generation mechanism”. Further, the “EV mode”corresponds to a “first traveling mode”, and the “HV mode” correspondsto a “second traveling mode”.

FIG. 4 is a functional block diagram illustrating traveling control inthe hybrid vehicle in accordance with Embodiment 1 of the presentinvention. Each functional block shown in FIG. 4 can be implemented bycontrol device 100 executing software processing in accordance with apreset program. Alternatively, it is also possible to configure acircuit (hardware) having a function corresponding to the functionalblock inside control device 100.

Referring to FIG. 4, a state estimation unit 110 estimates the SOC ofpower storage device 10 based on battery data (Tb, Ib, Vb) frommonitoring unit 11. For example, state estimation unit 110 sequentiallycomputes an estimated SOC value (#SOC) of power storage device 10 basedon an integrated value of a charged/discharged amount of power storagedevice 10. The integrated value of the charged/discharged amount isobtained by time-integrating the product of battery current Ib andbattery voltage Vb (i.e., power). Alternatively, the estimated SOC value(#SOC) may be calculated based on the relationship between an opencircuit voltage (OCV) and the SOC.

A current load estimation unit 120 calculates a current load parameterMP indicating a thermal load on equipment due to passage of batterycurrent Ib, based on battery current Ib. In the present embodiment, byreflecting current load parameter MP to control of charging/dischargingof power storage device 10, heat generation in equipment constituting anelectric system (i.e., parts constituting power control unit 20, such asa reactor, a capacitor, and a switching element) is controlled not tobecome excessive.

As shown in FIG. 5, a thermal load on each equipment is generallydesigned by defining a limit line indicating an allowable time withrespect to a moving average value of a flowing current. That is, inaccordance with the level of the flowing current, an allowable time forwhich the current can continuously flow is designed beforehand, andcharging/discharging of power storage device 10 is limited as necessarysuch that a load indicated by the product of the flowing current and aflowing time does not exceed the limit line.

In the electric system shown in FIG. 1, a passing current of eachequipment has a magnitude in accordance with the magnitude of batterycurrent Ib. Therefore, current load parameter MP is defined as aparameter for quantitatively evaluating the thermal load on eachequipment due to passage of battery current Ib. Current load parameterMP is calculated by smoothing a time-shift of a square value of batterycurrent Ib using a low pass filter. For example, by employing a low passfilter of a first-order lag system, current load parameter MP iscalculated for each regular control cycle, in accordance with thefollowing equation (1):MP(n)=(K−1)/K·MP(n−1)+Ib ²(n)/K  (1)

In equation (1), MP(n) is a calculated value in a present control cycle,and MP(n−1) is a calculated value in a previous control cycle. Ib²(n) isa square value of battery current Ib in the present control cycle. Acoefficient K is a value determined by a time constant of thefirst-order lag and the control cycle. The greater coefficient K is, thegreater the time constant is. The greater the time constant is, thegreater a change in current load parameter MP with respect to a changein the square value of battery current Ib is smoothed. It is to be notedthat, in the case of a large current, the time constant is preferablyset to a value lower than usual, for evaluation of the thermal load.Further, in the case of heat dissipation (MP(n−1)>Ib²(n)), the timeconstant is set to a value lower than that in the case of heatgeneration (MP(n−1)<Ib²(n)).

Referring to FIG. 4 again, a traveling mode selection unit 205 isconfigured to select one of the HV mode and the EV mode in response tothe SOC of power storage device 10.

FIG. 6 shows one example of traveling mode selection with respect to SOCshifts in hybrid vehicle 5.

Referring to FIG. 6, in hybrid vehicle 5, when the vehicle startstraveling (at time t1), power storage device 10 has been externallycharged to almost an SOC upper limit value Smax. When an ignition switchis turned on and hybrid vehicle 5 starts traveling, the EV mode isselected because the estimated SOC value (#SOC) is higher than a modedetermination value Sth. It is to be noted that the SOC control range ateach timing ranges from a control lower limit value SOCl to a controlupper limit value SOCu. The intermediate value between control lowerlimit value SOCl and control upper limit value SOCu is a control centralvalue SOCr. As described above, if the SOC becomes lower than thecontrol range, charging of power storage device 10 during traveling ofthe vehicle is requested.

Due to traveling in the EV mode, the SOC of power storage device 10 isgradually reduced. During the EV mode, control central value SOCr in theSOC control range is set corresponding to the estimated SOC value (#SOC)at the present moment. That is, in the EV mode, as the SOC is reduced,the SOC control range also becomes lower. As a result, during the EVmode, engine 18 is not started for the purpose of charging power storagedevice 10.

If the estimated SOC value (#SOC) is reduced to mode determination valueSth (at time t2), the traveling mode shifts from the EV mode to the HVmode. When the traveling mode shifts to the HV mode, control centralvalue SOCr is set to a constant value for the HV mode. Thereby, controllower limit value SOCl is also maintained constant. As a result, in theHV mode, if the SOC is reduced, engine 18 (FIG. 1) is started foroperation, and power storage device 10 is charged using electric powergenerated by motor generator MG1. Consequently, the SOC startsincreasing and is maintained within the SOC control range (SOCl toSOCu).

If the HV mode is forcibly selected by operating selection switch 26during the EV mode (#SOC>Sth), charging/discharging of power storagedevice 10 is controlled to maintain the SOC at that moment. That is, theSOC control range is set to fix control central value SOCr at theestimated SOC value (#SOC) when selection switch 26 is operated.

Then, when hybrid vehicle 5 finishes traveling, the driver couplesconnector portion 3 (FIG. 1) to hybrid vehicle 5, and thus externalcharging is started (at time t3). Thereby, the SOC of power storagedevice 10 is increased.

Referring to FIG. 4 again, in a period when the estimated SOC value(#SOC) estimated by state estimation unit 110 is higher than modedetermination value Sth, traveling mode selection unit 205 selects theEV mode. On the other hand, if the estimated SOC value is reduced tomode determination value Sth while the EV mode is performed, travelingmode selection unit 205 switches the traveling mode from the EV mode tothe HV mode. However, when selection switch 26 is operated by the user,traveling mode selection unit 205 forcibly selects the HV mode or the EVmode in accordance with the user's operation. Traveling mode selectionunit 205 outputs a traveling mode signal MD indicating which of the EVmode and the HV mode is selected.

A charging/discharging control unit 150 sets an input power upper limitvalue Win and an output power upper limit value Wout based on the stateof power storage device 10. As common control of charging/discharging,if the estimated SOC value (#SOC) is reduced, output power upper limitvalue Wout is limited to be less than a default value, whereas if theestimated SOC value (#SOC) is increased, input power upper limit valueWin is limited to be less than a default value. Further, if batterytemperature Tb is changed to a low temperature or a high temperature,input power upper limit value Win and output power upper limit valueWout are suppressed when compared with those at ordinary temperature.

In addition, charging/discharging control unit 150 sets input powerupper limit value Win and output power upper limit value Wout by furtherreflecting current load parameter MP calculated by current loadestimation unit 120. For example, if current load parameter MP is lowerthan a determination value (threshold value) Mt, charging/dischargingcontrol unit 150 does not limit output power upper limit value Wout fromthe aspect of the current load (thermal load due to the current),whereas if current load parameter MP exceeds determination value Mt,charging/discharging control unit 150 limits output power upper limitvalue Wout.

As is understood from equation (1) for calculating current loadparameter MP, a certain time lag is required before a reduction inbattery current Ib is reflected to current load parameter MP. Therefore,once current load parameter MP exceeds determination value Mt, even ifbattery current Ib is reduced by limiting output power from powerstorage device 10, it takes a certain time before current load parameterMP is decreased. During this period, limitation on output power upperlimit value Wout is continued.

It is not necessary to use all of the SOC of power storage device 10,battery temperature Tb, and battery current Ib (current load parameterMP) to set input power upper limit value Win and output power upperlimit value Wout. Charging/discharging control unit 150 is configured tovariably set input power upper limit value Win and output power upperlimit value Wout, based on at least one of the SOC of power storagedevice 10 and battery current Ib to be reflected to current loadparameter MP.

Further, charging/discharging control unit 150 determines whether or notpower storage device 10 should be charged during traveling of thevehicle. As described above, in the EV mode, a request to charge powerstorage device 10 is not generated. In the HV mode, a request to chargepower storage device 10 is generated in accordance with the relationshipbetween the estimated SOC value (#SOC) and the SOC control range (SOClto SOCu).

A motor traveling upper limit vehicle speed setting unit 210 sets anupper limit vehicle speed VMmax in motor traveling using only the outputof motor generator MG2, for each of the EV mode and the HV mode, basedon traveling mode signal MD.

A traveling control unit 200 calculates a vehicle driving force and avehicle braking force required for entire hybrid vehicle 5, in responseto a vehicle state of hybrid vehicle 5 and a driver's operation. Thedriver's operation includes an amount of depression of an acceleratorpedal (not shown), a position of a shift lever (not shown), an amount ofdepression of a brake pedal (not shown), and the like.

Then, traveling control unit 200 controls output distribution amongmotor generators MG1, MG2 and engine 18 to achieve the required vehicledriving force or vehicle braking force. In accordance with the controlon output distribution, output requests for motor generators MG1, MG2and an output request for engine 18 are determined. As part of thecontrol on output distribution, one of motor traveling and engine usedtraveling is selected. Further, the output requests for motor generatorsMG1, MG2 are set by placing a limitation such that charging/dischargingof power storage device 10 is not performed within a power range inwhich power storage device 10 can be charged/discharged (Win to Wout).That is, when it is not possible to ensure the output power of powerstorage device 10, the output by motor generator MG2 is limited.Further, if a request to charge power storage device 10 is generatedfrom charging/discharging control unit 150, the output of engine 18 tobe used to generate electric power in motor generator MG1 is ensured.

A distribution unit 250 computes torques and rotation speeds of motorgenerators MG1, MG2, in response to the output requests for motorgenerators MG1, MG2 set by traveling control unit 200. Then,distribution unit 250 outputs control commands for the torques androtation speeds to an inverter control unit 260, and outputs a controlcommand value for DC voltage Vh to a converter control unit 270.

On the other hand, distribution unit 250 generates an instruction tocontrol the engine which indicates engine power and a target enginerotation speed determined by traveling control unit 200. In accordancewith the instruction to control the engine, fuel injection, ignitiontiming, valve timing, and the like of engine 18 not shown arecontrolled.

Inverter control unit 260 generates switching commands PWM1 and PWM2 fordriving motor generators MG1 and MG2, in response to the controlcommands from distribution unit 250. Switching commands PWM1 and PWM2are output to inverters 8-1 and 8-2, respectively.

Converter control unit 270 generates a switching command PWC such thatDC voltage Vh is controlled in accordance with the control command fromdistribution unit 250. By voltage conversion of converter 6 inaccordance with switching command PWC, charging/discharging power forpower storage device 10 is controlled.

In this way, traveling control for hybrid vehicle 5 with improved energyefficiency is achieved in response to the vehicle state and the driver'soperation.

Selection of motor traveling and hybrid traveling by traveling controlunit 200 will be described in detail, with reference to FIG. 7.

Referring to FIG. 7, the axis of abscissas represents a vehicle speed Vof hybrid vehicle 5, and the axis of ordinates represents a drivingtorque T. Vehicle speed V and driving torque T define a maximum outputline 300 of hybrid vehicle 5.

Maximum output line 300 is composed of a straight line at T=Tmax (upperlimit torque), a straight line at V=Vmax (upper limit vehicle speed),and a curved line in a region of T<Tmax and V<Vmax. The curved lineportion in maximum output line 300 corresponds to upper limit outputpower.

Maximum output lines 340 and 350 in motor traveling are defined for theHV mode and the EV mode, respectively. As with maximum output line 300,each of maximum output lines 340 and 350 is composed of straight lineportions defining an upper limit torque TMmax and upper limit vehiclespeed VMmax and a curved line portion defining upper limit output power,in motor traveling.

In the HV mode, if hybrid vehicle 5 has an operating point (vehiclespeed, torque) inside maximum output line 340, motor traveling isselected, and the vehicle driving force is ensured using only the outputof motor generator MG. On the other hand, if hybrid vehicle 5 has anoperating point outside maximum output line 340, the vehicle drivingforce is ensured by hybrid traveling in which engine 18 is started.

In the HV mode in which the SOC is maintained, a region for motortraveling is set to be relatively small to drive engine 18 in a regionwith high engine efficiency. In contrast, in the EV mode, maximum outputline 350 is set to be relatively large to actively select motortraveling.

For example, in the HV mode, hybrid traveling is selected at each ofoperating points 302 to 306. On the other hand, in the EV mode, motortraveling is selected at operating point 302. However, even in the EVmode, hybrid traveling is selected at operating point 304 where anoutput torque higher than that at operating point 302 is requested,because it is outside maximum output line 350. That is, engine 18 isstarted. Further, when a request to charge power storage device 10 isgenerated as described above, even if an operating point is insidemaximum output line 340, 350, engine 18 is operated to be used for powergeneration in motor generator MG1.

The curved line portion of maximum output line 340, 350 changes inresponse to output power upper limit value Wout of power storage device10. Specifically, when output power upper limit value Wout is limited, aregion inside maximum output line 340, 350, that is, a region in whichmotor traveling is selected, is narrowed.

In particular, when output power upper limit value Wout is limited by anincrease in current load parameter MP, there is a possibility that,while the EV mode is selected because of the sufficient SOC, engine 18is frequently started. This can cause a reduction in energy efficiencyof hybrid vehicle 5.

Further, when the vehicle speed increases and shifts from operatingpoint 302 to operating point 306, hybrid traveling is selected becauseV>VMmax is obtained and operating point 306 is outside maximum outputline 350. That is, when vehicle speed V exceeds motor traveling upperlimit vehicle speed VMmax. starting of engine 18 is instructed andhybrid traveling is selected. As a result, a further increase in theoutput of motor generator MG2 is prohibited.

In a high rotation speed region, efficiency of motor generators MG1, MG2(rotating electric machine) is reduced due to high iron loss. Further,at a high vehicle speed, driving resistance is increased, and thereby ahigh load state is likely to be caused. Thus, in motor traveling at ahigh vehicle speed, the energy efficiency (fuel efficiency) of hybridvehicle 5 is deteriorated, and a current for obtaining the same output,that is, battery current Ib, is increased. Therefore, by setting motortraveling upper limit vehicle speed VMmax, vehicle traveling iscontrolled to avoid continuous motor traveling in a high speed region.

In the present embodiment, motor traveling upper limit vehicle speedVMmax (EV) in the EV mode is set to be lower than motor traveling upperlimit vehicle speed VMmax (HV) in the HV mode.

FIG. 8 shows a procedure of processing for traveling control in hybridvehicle 5 in accordance with the embodiment of the present invention.Processing in each step shown in FIG. 8 can be implemented by controldevice 100 executing a predetermined program stored beforehand, orcausing a dedicated electronic circuit to operate. A series of controlprocessing shown in FIG. 8 is repeatedly performed for each regularcontrol cycle.

Referring to FIG. 8, by step S100, control device 100 estimates the SOCof power storage device 10. That is, in step S100, the estimated SOCvalue (#SOC) is calculated by the same function as that of stateestimation unit 110 in FIG. 4. Further, in step S110, control device 100calculates current load parameter MP based on battery current Ib, inaccordance with (1) described above. That is, processing by step S110corresponds to the function of current load estimation unit 120 in FIG.4.

By step S120, control device 100 sets input power upper limit value Winand output power upper limit value Wout of power storage device 10. Thatis, in step S120, input power upper limit value Win and output powerupper limit value Wout are variably set by the same function as that ofcharging/discharging control unit 150 in FIG. 4. As described above, ifcurrent load parameter MP exceeds threshold value Mt, input power upperlimit value Win and output power upper limit value Wout are limited.Further, by step S140, control device 100 selects one of the HV mode andthe EV mode as the traveling mode of hybrid vehicle 5, mainly based onthe SOC of power storage device 10, by the same function as that oftraveling mode selection unit 205 in FIG. 4.

By step S150, control device 100 sets motor traveling upper limitvehicle speed VMmax of hybrid vehicle 5, in response to the state ofpower storage device 10. Processing by step S150 corresponds to thefunction of motor traveling upper limit vehicle speed setting unit 210in FIG. 4.

FIG. 9 is a flowchart illustrating the processing by step S150 in FIG. 8in detail.

Referring to FIG. 9, in step S152, control device 100 determines whetheror not the traveling mode is the EV mode. If the traveling mode is theEV mode (YES in S152), control device 100 advances the processing tostep S153. In step S153, motor traveling upper limit vehicle speed VMmaxfor the EV mode is set.

On the other hand, if the traveling mode is the HV mode (NO in S152), bystep S158, control device 100 sets motor traveling upper limit vehiclespeed VMmax for the HV mode. As described above, motor traveling upperlimit vehicle speed VMmax for the HV mode is higher than motor travelingupper limit vehicle speed VMmax for the EV mode.

Referring to FIG. 8 again, by step S160, control device 100 controlsoutput distribution among motor generators MG1, MG2, and engine 18, bythe same function as that of traveling control unit 200 in FIG. 4. Inthe control on output distribution in step S160, maximum output lines340, 350 are set. Then, in accordance with maximum output lines 340,350, one of motor traveling and engine used traveling is selected, thatis, whether or not engine 18 should be operated is determined. Further,output requests for motor generators MG1, MG2 and an output request forengine 18 are determined.

In step S170, control device 100 controls engine 18 and motor generatorsMG1, MG2, in accordance with control commands for the engine, MG1, andMG2, respectively, according to the control on output distribution instep S160.

Then, by step S180, control device 100 displays a vehicle speed range inwhich motor traveling is applicable, on display area 105. For example,on display area 105, an entire vehicle speed range of hybrid vehicle 5is displayed, and the vehicle speed range in which motor traveling isapplicable, of the entire vehicle speed range, is additionally displayedin a specific color (for example, green). Display area 105 may becomposed using a portion (for example, a numeric panel portion) of aspeedometer (not shown).

Thus, guidance information for spontaneously continuing motor traveling,that is, information for assisting so-called eco-drive, can be providedto the driver. It is to be noted that the vehicle speed range in whichmotor traveling is applicable can be set, for example, to be a vehiclespeed range lower than motor traveling upper limit vehicle speed VMmax.As described above, the SOC and/or current load parameter MP are/isreflected to motor traveling upper limit vehicle speed VMmax.Alternatively, a vehicle speed range defined by maximum output lines 340and 350, to which motor traveling upper limit vehicle speed VMmax isreflected, may be displayed on display area 105 to correspond to anoperating point at present. Thus, the vehicle speed range in which motortraveling is applicable to be displayed on display area 105 can bedetermined at least based on motor traveling upper limit vehicle speedVMmax.

As has been described above, in the hybrid vehicle in accordance withEmbodiment 1, in the EV mode in which electric power of power storagedevice 10 is actively used, motor traveling upper limit vehicle speedVMmax is set to be lower than that in the HV mode. This can prevent asituation where, due to motor traveling in the high-speed region, outputpower upper limit value Wout is limited by the SOC and/or current loadparameter MP. That is, a period for which the vehicle can travel withoutlimitation on output power upper limit value Wout can be ensuredsufficiently. As a result, a range in which motor traveling canaccommodate a driver's request for acceleration is relatively widened,and thus motor traveling can be applied for a long period of time, withthe start of engine 18 being suppressed. That is, since a frequency ofoperating engine 18 in the EV mode can be reduced, deterioration inemission can be avoided and traveling with high energy efficiency can beperformed. Consequently, motor traveling upper limit vehicle speed VMmaxcan be set appropriately such that opportunities for motor traveling canbe ensured appropriately.

On the other hand, in the HV mode originally having a high frequency ofoperating engine 18, opportunities for charging power storage device 10are provided in the region with high engine efficiency. Therefore,energy efficiency of entire hybrid vehicle 5 can be improved by allowingmotor traveling up to a high vehicle speed region.

Further, by displaying the vehicle speed range in which motor travelingis applicable on display area 105, information for assisting eco-driveby applying motor traveling can be provided to the driver.

Embodiment 2

In Embodiment 2, motor traveling upper limit vehicle speed VMmax in theEV mode in the hybrid vehicle in Embodiment 1 is changed in response tothe state of power storage device 10. This further prevents output powerupper limit value Wout from being limited. That is, since fundamentalportions of the system configuration and traveling control for thehybrid vehicle are common to those in Embodiment 1, Embodiment 2 willdescribe differences from Embodiment 1.

FIG. 10 is a conceptual diagram illustrating setting of a motortraveling upper limit vehicle speed in a hybrid vehicle in accordancewith Embodiment 2.

Referring to FIG. 10, in the hybrid vehicle in accordance withEmbodiment 2, motor traveling upper limit vehicle speed VMmax in the EVmode is changed by motor traveling upper limit vehicle speed settingunit 210 (FIG. 4), in response to the state of power storage device 10.This reduces the frequency with which output power upper limit valueWout is limited.

FIG. 11 is a flowchart illustrating a procedure of processing forsetting motor traveling upper limit vehicle speed VMmax in the hybridvehicle in accordance with Embodiment 2. In the traveling control forthe hybrid vehicle in accordance with Embodiment 2, when the flowchartshown in FIG. 8 is performed for each predetermined cycle, processing inaccordance with the flowchart of FIG. 11 is performed instead of theflowchart of FIG. 9, as the processing in step S150.

Referring to FIG. 11, in step S152, control device 100 determineswhether or not the traveling mode is the EV mode. If the traveling modeis the EV mode (YES in S152), control device 100 advances the processingto step S154. In step S154, a motor traveling upper limit vehicle speedVMmax(1) is set in response to current load parameter MP, in accordancewith the property shown in FIG. 12.

Referring to FIG. 12, the axis of abscissas, ΔMP, represents adifference between current load parameter MP and threshold value Mt atwhich limitation on output power upper limit value Wout is started. Thatis, ΔMP=Mt−MP.

In the case of ΔMP>M1, that is, when current load parameter MP issufficiently small, upper limit vehicle speed VMmax is set to a defaultvalue. On the other hand, as current load parameter MP is increased andapproaches threshold value Mt, motor traveling upper limit vehicle speedVMmax is reduced in a stepwise manner. By preparing a map correspondingto FIG. 12 beforehand, motor traveling upper limit vehicle speed VMmaxcan be set corresponding to current load parameter MP. Alternatively,motor traveling upper limit vehicle speed VMmax may be continuouslyreduced corresponding to reduction in ΔMP.

Referring to FIG. 11 again, in step S155, control device 100 sets amotor traveling upper limit vehicle speed VMmax(2) in response to theestimated SOC value (#SOC), in accordance with the property shown inFIG. 13.

Referring to FIG. 13, the axis of abscissas represents the estimated SOCvalue (#SOC) calculated by state estimation unit 110. In a region withhigh SOC (#SOC>S1), upper limit vehicle speed VMmax is set to a defaultvalue. On the other hand, if #SOC becomes lower than a determinationvalue 51, motor traveling upper limit vehicle speed VMmax is reduced ina stepwise manner corresponding to reduction in the SOC. By preparing amap corresponding to FIG. 13 beforehand, motor traveling upper limitvehicle speed VMmax can be set corresponding to the estimated SOC value(#SOC). It is to be noted that motor traveling upper limit vehicle speedVMmax may be continuously reduced corresponding to reduction in the SOC.

Referring to FIG. 11 again, by step S156, control device 100 sets aminimum value of motor traveling upper limit vehicle speeds VMmax(1) andVMmax(2), as motor traveling upper limit vehicle speed VMmax.

On the other hand, if the traveling mode is the HV mode (NO in S152), bystep S158, control device 100 sets motor traveling upper limit vehiclespeed VMmax for the HV mode. As described above, in the HV mode,traveling of the vehicle is performed to maintain a constant SOC ofpower storage device 10, that is, without actively using battery power.Therefore, motor traveling upper limit vehicle speed VMmax in the HVmode is generally fixed at a constant value with respect to the state ofpower storage device 10. It is to be noted that a range in which motortraveling upper limit vehicle speed VMmax is changed in the EV mode ison a side with a speed lower than motor traveling upper limit vehiclespeed VMmax in the HV mode.

FIG. 14 shows one example of vehicle speed limitation for hybrid vehicle5 in continuous motor traveling in the EV mode.

Referring to FIG. 14, due to continued motor traveling, the estimatedSOC value (#SOC) is gradually reduced over time. Due to continuousdischarging of power storage device 10 associated with motor traveling,current load parameter MP is also gradually increased in response tobattery current Ib.

Motor traveling upper limit vehicle speed VMmax(1) in response tocurrent load parameter MP is sequentially set in accordance with the mapshown in FIG. 12. Similarly, motor traveling upper limit vehicle speedVMmax(2) in response to the estimated SOC value (#SOC) is sequentiallyset in accordance with the map shown in FIG. 13. At each control cycle,the minimum value of VMmax(1) and VMmax(2) is set as motor travelingupper limit vehicle speed VMmax.

In response to an increase in current load parameter MP, VMmax(1) isreduced at each of times t1, t3, t4, and t5. On the other hand, inresponse to a reduction in the estimated SOC value (#SOC), VMmax(2) isreduced at each of times t2 and t6. Since motor traveling upper limitvehicle speed VMmax is reduced by a reduction in VMmax(1) or VMmax(2),the vehicle speed of hybrid vehicle 5 is gradually limited and reduced.

When current load parameter MP reaches threshold value Mt at time t7,output power upper limit value Wout is lowered. As a result, engine 18is started, and the traveling mode shifts from motor traveling to hybridtraveling. In hybrid traveling, the output by motor generator MG2 isreduced. Thus, the output power from power storage device 10 and batterycurrent Ib are also reduced. Consequently, current load parameter MPstarts decreasing.

It is to be noted that, to prevent engine 18 from being frequentlystarted and stopped repeatedly, hysteresis is provided in thedetermination for shifting to motor traveling again. Thus, hybridtraveling is selected until current load parameter MP is sufficientlyreduced and the limitation on output power upper limit value Wout islifted, or the vehicle speed and/or driving torque of hybrid vehicle 5are/is reduced.

In traveling control in which motor traveling upper limit vehicle speedVMmax is fixed, current load parameter MP is expected to reach thresholdvalue Mt earlier when compared with the example shown in FIG. 14. Onceoutput power upper limit value Wout is limited, there is a possibilitythat engine 18 is thereafter started more frequently. That is, it isunderstood that, in hybrid vehicle 5 in accordance with Embodiment 2, aperiod for which the output power from power storage device 10 can beensured can be increased by changing (reducing) motor traveling upperlimit vehicle speed VMmax in response to the state of power storagedevice 10.

As has been described above, in hybrid vehicle 5 in accordance withEmbodiment 2, in the EV mode in which electric power of power storagedevice 10 is actively used, motor traveling upper limit vehicle speedVMmax can be variably set in response to the state of power storagedevice 10 (the SOC and current load parameter MP). Thereby, a period forwhich the vehicle can travel without limitation on output power upperlimit value Wout by the SOC and/or current load parameter MP can beensured sufficiently, when compared with Embodiment 1. As a result,since the frequency of operating engine 18 in the EV mode can be furtherreduced, deterioration in emission can be avoided and traveling withhigh energy efficiency can be performed.

It is to be noted that Embodiment 2 has described an example in whichmotor traveling upper limit vehicle speed VMmax is set using both of theSOC of power storage device 10 and current load parameter MP. From theviewpoint of protecting equipment, output power upper limit value Wouttends to be limited more strictly by current load parameter MP. Further,when output limitation by current load parameter MP is started, even ifbattery current Ib is reduced, a certain time lag occurs before theoutput limitation is lifted. Therefore, it is also possible to set motortraveling upper limit vehicle speed VMmax in response to only currentload parameter MP. In this case, it is only required to omit theprocessing in step S155 in the flowchart of FIG. 11 and set asVMmax=VMmax(1) in step S156. Alternatively, motor traveling upper limitvehicle speed VMmax may be set as VMmax=VMmax(2) based on only the SOC.

However, if motor traveling upper limit vehicle speed VMmax is setconsidering both of the SOC and current load parameter MP, it isexpected that cases where output power upper limit value Wout is limitedwill be reduced. That is, the effect exhibited by the present embodimentcan be enjoyed more reliably.

It is noted for confirmation that, in Embodiments 1 and 2, theconfiguration of power control unit 20 is not limited to the oneillustrated in FIG. 1, and any configuration is applicable as long as itis a configuration for driving motor generators MG1, MG2 using electricpower of power storage device 10. It is also noted for confirmation thatthe configuration of the drive system for hybrid vehicle 5 is notlimited to the one illustrated in FIG. 1. Similarly, it is also possibleto apply a “power generation mechanism” different from motor generatorMG1 in FIG. 1 as long as it is configured to generate charging power forthe power storage device using the output of the engine.

Further, in Embodiment 2, it is also possible to apply any otherparameter to which battery current Ib is reflected, instead of currentload parameter MP. As long as it is a state quantity or parameterrelated to power storage device 10 which is reflected to limitation onoutput power upper limit value Wout, it can be used instead of currentload parameter MP. This is because, by changing the upper limit vehiclespeed in traveling of the vehicle using only the rotating electricmachine (motor generator MG2) in response to such a parameter, a periodfor which output power upper limit value Wout is limited can be reduced,as in the traveling control for the hybrid vehicle as described above.

It should be understood that the embodiments disclosed herein areillustrative and non-restrictive in every respect. The scope of thepresent invention is defined by the scope of the claims, rather than thedescription above, and is intended to include any modifications withinthe scope and meaning equivalent to the scope of the claims.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a hybrid vehicle capable oftraveling using only an output of a rotating electric machine utilizingelectric power of a vehicle-mounted power storage device.

REFERENCE SIGNS LIST

3: connector portion, 5: hybrid vehicle, 6: converter, 7: system mainrelay, 8: inverter, 10: power storage device, 11: monitoring unit, 12:temperature sensor, 13, 16: voltage sensor, 14: current sensor, 18:engine, 20: power control unit, 22: motive power split mechanism, 24F:driving wheel, 26: selection switch, 30: external charging unit, 30 a:current control unit, 30 b: voltage conversion unit, 35: connectorreceiving portion, 35 a: coupling detection sensor, 95: reductionmechanism, 100: control device (ECU), 110: state estimation unit, 120:current load estimation unit, 150: charging/discharging control unit,200: traveling control unit, 202: sun gear, 204: pinion gear, 205:traveling mode selection unit, 206: carrier, 208: ring gear, 210: motortraveling upper limit vehicle speed setting unit, 250: distributionunit, 260: inverter control unit, 270: converter control unit, 300:maximum output line (vehicle), 302, 304, 306: operating point, 340:maximum output line (motor traveling/HV mode), 350: maximum output line(motor traveling/EV mode), C: smoothing capacitor, CNL: negative chargeline, CON: coupling signal, CPL: positive charge line, Ib: batterycurrent, K: smoothing coefficient, MD: traveling mode signal, MG1: motorgenerator (power generation mechanism), MG2: motor generator (rotatingelectric machine), MP: current load parameter, Mt: threshold value, PWC,PWM1, PWM2: switching command, SE: relay control signal, SOCl to SOCu:SOC control range, SOCr: control central value, Smax: SOC upper limitvalue, Smin: SOC lower limit value, Sth: mode determination value, T:vehicle driving torque, TMmax: upper limit torque (motor traveling), Tb:battery temperature, V: vehicle speed, VMmax: motor traveling upperlimit vehicle speed, Vb: battery voltage, Vh: system voltage, Vmax:upper limit vehicle speed (vehicle), Win: input power upper limit value,Wout: output power upper limit value.

The invention claimed is:
 1. A hybrid vehicle, comprising: a rotatingelectric machine for generating a vehicle driving force; a power storagedevice mounted in the vehicle; a power control unit for performing powerconversion between said power storage device and said rotating electricmachine; an internal combustion engine for generating a vehicle drivingforce; an external charging unit for charging said power storage deviceby a power source external to the vehicle; and a control device forcontrolling traveling of the vehicle, said control device including atraveling mode selection unit for selecting, in response to a state ofcharge of said power storage device, one of a first traveling mode inwhich said internal combustion engine and said rotating electric machineare used such that the vehicle travels mainly using an output of saidrotating electric machine irrespective of a residual capacity of saidpower storage device, and a second traveling mode in which said internalcombustion engine and said rotating electric machine are used such thatthe vehicle travels with the residual capacity of said power storagedevice being maintained within a predetermined control range, an upperlimit vehicle speed setting unit for setting an upper limit vehiclespeed for traveling of the vehicle using only the output of saidrotating electric machine, in response to the traveling mode selected bysaid traveling mode selection unit, and a traveling control unit forcontrolling traveling of the vehicle to use both of outputs of saidinternal combustion engine and the rotating electric machine, if avehicle speed exceeds said upper limit vehicle speed, said upper limitvehicle speed setting unit setting said upper limit vehicle speed insaid first traveling mode to be lower than said upper limit vehiclespeed in said second traveling mode.
 2. The hybrid vehicle according toclaim 1, wherein said traveling control unit controls said rotatingelectric machine and said internal combustion engine in said firsttraveling mode such that, if said hybrid vehicle has a torque and avehicle speed inside a first region which is defined by a combination ofsaid torque and said vehicle speed, the vehicle travels using only theoutput of said rotating electric machine, and if said hybrid vehicle hasa torque and a vehicle speed outside said first region, the vehicletravels using both of the outputs of said rotating electric machine andsaid internal combustion engine, and controls said rotating electricmachine and said internal combustion engine in said second travelingmode such that, if said hybrid vehicle has a torque and a vehicle speedinside a second region which is defined by a combination of said torqueand said vehicle speed, the vehicle travels using only the output ofsaid rotating electric machine, and if said hybrid vehicle has a torqueand a vehicle speed outside said second region, the vehicle travelsusing both of the outputs of said rotating electric machine and saidinternal combustion engine, and said first and second regions are setcorresponding to a maximum output line in a traveling only by saidrotating electric machine with said upper limit vehicle speed set bysaid upper limit vehicle speed setting unit reflected, in said first andsecond traveling mode, respectively.
 3. The hybrid vehicle according toclaim 1, wherein, in said first traveling mode, said upper limit vehiclespeed setting unit variably sets said upper limit vehicle speed within arange lower than said upper limit vehicle speed in said second travelingmode, based on at least one of the state of charge and an input/outputcurrent of said power storage device.
 4. The hybrid vehicle according toclaim 3, wherein said control device further includes a state-of-chargeestimation unit for calculating an estimated residual capacity value ofsaid power storage device based on an output of a sensor arranged insaid power storage device, a current load estimation unit forcalculating a current load parameter indicating a thermal load onequipment due to passage of said input/output current of said powerstorage device, based on said input/output current, and acharging/discharging control unit for variably setting an output powerupper limit value of said power storage device based on the calculatedestimated residual capacity value and current load parameter, and insaid first traveling mode, said upper limit vehicle speed setting unitvariably sets said upper limit vehicle speed, at least based on saidcalculated current load parameter.
 5. The hybrid vehicle according toclaim 4, wherein said upper limit vehicle speed setting unit sets saidupper limit vehicle speed in said first traveling mode, in accordancewith a minimum value of a first upper limit speed variably set inresponse to said current load parameter and a second upper limit speedvariably set in response to said estimated residual capacity value. 6.The hybrid vehicle according to claim 1, further comprising a displayunit for causing a driver to visually recognize vehicle information,wherein said display unit includes a display area for displaying avehicle speed range in which traveling of the vehicle using only theoutput of said rotating electric machine is applicable, at least basedon said upper limit vehicle speed set by said upper limit vehicle speedsetting unit.
 7. The hybrid vehicle according to claim 1, furthercomprising a power generation mechanism configured to generate chargingpower for said power storage device using the output of said internalcombustion engine, wherein, in said second traveling mode, if theresidual capacity of said power storage device becomes lower than saidcontrol range, said traveling control unit controls said rotatingelectric machine and said internal combustion engine such that thecharging power for said power storage device is generated by said powergeneration mechanism.
 8. A control method for a hybrid vehicle includinga rotating electric machine and an internal combustion engine each forgenerating a vehicle driving force, a power storage device mounted inthe vehicle, a power control unit for performing power conversionbetween said power storage device and said rotating electric machine,and an external charging unit for charging said power storage device byan external power source, said control method comprising the steps of:selecting, in response to a state of charge of said power storagedevice, one of a first traveling mode in which said internal combustionengine and said rotating electric machine are used such that the vehicletravels mainly using an output of said rotating electric machineirrespective of a residual capacity of said power storage device, and asecond traveling mode in which said internal combustion engine and saidrotating electric machine are used such that the vehicle travels withthe residual capacity of said power storage device being maintainedwithin a predetermined control range; setting an upper limit vehiclespeed for traveling of the vehicle using only the output of saidrotating electric machine, in response to the selected traveling mode;and controlling traveling of the vehicle to use both of outputs of saidinternal combustion engine and said rotating electric machine, if avehicle speed exceeds said upper limit vehicle speed, in said step ofsetting, said upper limit vehicle speed in said first traveling mode isset to be lower than said upper limit vehicle speed in said secondtraveling mode.
 9. The control method for the hybrid vehicle accordingto claim 8, wherein said step of selecting controls said rotatingelectric machine and said internal combustion engine in said firsttraveling mode such that, if said hybrid vehicle has a torque and avehicle speed inside a first region which is defined by a combination ofsaid torque and said vehicle speed, the vehicle travels using only theoutput of said rotating electric machine, and if said hybrid vehicle hasa torque and a vehicle speed outside said first region, the vehicletravels using both of the outputs of said rotating electric machine andsaid internal combustion engine, and controls said rotating electricmachine and said internal combustion engine in said second travelingmode such that, if said hybrid vehicle has a torque and a vehicle speedinside a second region which is defined by a combination of said torqueand said vehicle speed, the vehicle travels using only the output ofsaid rotating electric machine, and if said hybrid vehicle has a torqueand a vehicle speed outside said second region, the vehicle travelsusing both of the outputs of said rotating electric machine and saidinternal combustion engine, and said first and second regions are setcorresponding to a maximum output line in a traveling only by saidrotating electric machine with said upper limit vehicle speed set bysaid step of setting reflected, in said first and second traveling mode,respectively.
 10. The control method for the hybrid vehicle according toclaim 8, wherein, in said first traveling mode, said step of settingvariably sets said upper limit vehicle speed within a range lower thansaid upper limit vehicle speed in said second traveling mode, based onat least one of the state of charge and an input/output current of saidpower storage device.
 11. The control method for the hybrid vehicleaccording to claim 10, further comprising the steps of: calculating anestimated residual capacity value of said power storage device based onan output of a sensor arranged in said power storage device; calculatinga current load parameter indicating a thermal load on equipment due topassage of said input/output current of said power storage device, basedon said input/output current; and variably setting an output power upperlimit value of said power storage device based on the calculatedestimated residual capacity value and current load parameter, and insaid first traveling mode, said step of setting said upper limit vehiclespeed variably sets said upper limit vehicle speed, at least based onsaid calculated current load parameter.
 12. The control method for thehybrid vehicle according to claim 11, wherein said step of settingincludes the steps of variably setting a first upper limit speed inresponse to said current load parameter, variably setting a second upperlimit speed in response to said estimated residual capacity value, andsetting said upper limit vehicle speed in said first traveling mode inaccordance with a minimum value of said first upper limit speed and saidsecond upper limit speed.
 13. The control method for the hybrid vehicleaccording to claim 8, wherein said hybrid vehicle further includes adisplay unit for causing a driver to visually recognize vehicleinformation, and said control method further comprises the step ofdisplaying a vehicle speed range in which traveling of the vehicle usingonly the output of said rotating electric machine is applicable on saiddisplay unit, at least based on said set upper limit vehicle speed. 14.The control method for the hybrid vehicle according to claim 8, whereinsaid hybrid vehicle further includes a power generation mechanismconfigured to generate charging power for said power storage deviceusing the output of said internal combustion engine, and in said secondtraveling mode, if the residual capacity of said power storage devicebecomes lower than said control range, said step of controlling controlssaid rotating electric machine and said internal combustion engine suchthat the charging power for said power storage device is generated bysaid power generation mechanism.